Transmissions with automatized shifting facilities have been used for an appreciable time in various types of motor vehicles. It has become known, in the case of such motor vehicles, that preference is given to the functioning of a startup clutch and/or a shifting clutch in a manner similar to the selection of the shifting paths as well as the in and out positioning of the transmission gear stages with the aid of hydraulic pressure powered activators. These activators are usually constructed as piston-cylinder assemblies. Contrary thereto, motor vehicles are also known, wherein a start clutch and/or a shifting clutch or only those elements of the transmission, which serve for the selection between the in and out clutch positioning, would be shifted by auxiliary means.
In the case of the necessary transmission elements to carry out the in and out clutch positioning in a transmission, the concern is with known clutch arrangements, such as sliding sleeves, which move axially beside gear-position sensitive idler gears on a transmission shaft. For the engagement of a gear position, such a clutch arrangement, is impelled by its actuator in the direction of the appointed idler gear and caused to rotate until its rotational speed coincides with that of this gear, so that as a final result, a rotational-secured and output drive effective connection is consummated between the idler gear and the transmission shaft. The release of a gear position is accomplished by a counter-directed activation of the clutch auxiliary aid.
The activation of the actuator is controlled by way of a transmission control apparatus which is guided by a control and regulation program. In order to properly operate the clutch and shifting commands, this program processes data regarding, for example, the driving situation, the state of shifting, as well as the power input desired by the driver of the motor vehicle.
Automatized shifting transmissions used in personal passenger cars are normally regulated by the braking action of synchronization apparatuses, which possess friction surfaces on the involved idler gears and also on separate synchronizations, which act between an idler gear and an axially slidable clutch apparatus. These frictional surfaces contactingly confront one another and are mutually counter-acting. During a shifting procedure, with the aid of frictional contact of these surfaces, an adjustment of speeds of rotation between a transmission input shaft and an assigned idler gear may be achieved, wherein the idler gear is specific to a new gear-stage in the transmission.
Counter to the above, where commercial vehicles are concerned, as a rule, automatic transmissions are put to use, which operate well without the above described synchronization apparatus and function by way of comparatively simply constructed dog clutches. In order to cause an idler gear of the transmission, which gear is designed for a specific speed ratio, to synchronizingly match the speed of rotation of an assigned transmission shaft, automatic transmissions, in this situation, are governed by a transmission brake, by way of which the transmission input shaft during an upshift procedure, can be braked down to the desired speed of rotation.
To effect a ratio change procedure in such a transmission, it is generally unnecessary for the specified speeds of rotation or the synchronization, which comply with the desired new gear ratio and the travel speed of the vehicle, is exactly attained. Much more, it is customary to adjust the transmission input speed to the required synchronizing speed SD of rotation so that its value falls within the confines of an engagement speed of rotation window F. The threshold borders of this speed of rotation window F consist of respective speeds of rotation which lie somewhat above and somewhat below the synchronization speed value. The upper speed of rotation is termed FO and the lower speed of rotation is termed FU.
Upon the operation of automatized transmissions, certain situations bring about their own effects. For example, in this respect, in the case of startup gearshifting taking place shortly prior to a vehicle coming to standstill, the situation can be that the synchronous speed of rotation SD—which can also be the above mentioned speed of rotation window F—appropriate for the new gear stage, lies at a value less than the no-load speed of rotation LD of the vehicle motor. Such a situation is shown in FIG. 2 of the attached illustrations.
Shiftings of the type shown in FIG. 2 are, generally carried out as downshifts wherein, when the clutch is partially or completely engaged, the speed of rotation of the transmission input shaft continues to be adjusted to the value of the speed of rotation window F, which said speed is less than the no-load speed LD of the drive motor.
Marked by a signal of a control apparatus in the transmission, which calls for the activation of a gear-stage engagement actuator, in the case of known transmission control procedures, the actual gear engagement procedure is released at that point of time t_1, wherein the transmission input speed of rotation GED has increased itself at the point of time t_1 from a minimum value to the lower threshold FU of the speed of rotation window F.
Since the gradient of the transmission input shaft speed of rotation GED, in a case of a partially or completely engaged clutch, is scarcely to be influenced and is comparatively steep, the gear engagement procedure itself, that is, the turn-fast connection of the gear-stage specific idler gear to its assigned transmission shaft, can be considered as complete, with the aid of the clutch means, only when the transmission input speed of rotation GED, in the sense of a rotation over-shoot (see Figures), has just exceeded the upper speed of rotation level FO of the speed of rotation window F. In such a situation, there would be present a large differential in speeds of rotation with a corresponding loss of comfort in the case of the turn-fast connection of the idler gear which is bound to its assigned transmission shaft. Disengaging the clutch in order to ease the actual engagement of the gear-stage and to improve the comfort of the shifting is carried out generally too late or not at all.
With the above as a background, the invention has the purpose of presenting a control method for an automatic transmission, by way of which, a comfortable shifting procedure can be carried out, particularly in a case where the synchronous speed of rotation relative to that of the transmission incoming speed of rotation for the gear chosen, is less than the speed of rotation for a no-load condition of the drive motor, i.e., an empty run.